The Role of NPY in Obesity
Dryden et al., conducted a study in 1995 using genetically obese rats to demonstrate the role of NPY in eating disorders such as obesity. The study revealed four underlying factors that contributed to obesity in rats: (1) an increase in glucocorticosteroid concentrations in plasma; (2) insensitivity or resistance to insulin; (3) mutation of leptin receptor; and (4) an increase in NPY mRNA and NPY release. Furthermore, these factors also correlate with each other. The sustained high levels of glucocorticosteroids stimulate gluconeogenesis, which subsequently causes an increase of blood glucose that activates the release of insulin to regulate glucose levels by causing its reuptake and storage as glycogen in the various tissues in the body. In the case of obesity, which researchers speculate to have a strong genetic and a dietary basis, insulin resistance prevents high blood glucose regulation, resulting in morbid levels of glucose and diabetes mellitus. Furthermore, high levels of glucocorticosteroids causes an increase of NPY by directly activating type II glucocorticosteroids receptors (which are activated only by relatively high levels of glucocorticosteroids) and, indirectly, by abolishing the negative feedback of corticotropin-releasing factor (CRF) on NPY synthesis and release. Meanwhile, obesity-induced insulin resistance and the mutation of the leptin receptor (ObRb) results in the abolition of inhibition of NPYergic activity and ultimately food intake via other negative feedback mechanisms to regulate them. Furthermore, obesity in rats was significantly reduced by adrenalectomy or hypophysectomy.
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